$$\eqalign{
& x \in \left( {A\backslash B} \right) \cap \left( {B\backslash A} \right) \cr
& \Rightarrow \left\{ \matrix{
x \in A\backslash B \hfill \cr
x \in B\backslash A \hfill \cr} \right. \cr
& \Rightarrow \left\{ \matrix{
x \in A \hfill \cr
x \notin B \hfill \cr
x \in B \hfill \cr
x \notin A \hfill \cr} \right. \Rightarrow Khong\,\,ton\,\,tai\,\,x\,\,thoa\,\,man \cr
& Vay\,\,\left( {A\backslash B} \right) \cap \left( {B\backslash A} \right) = \emptyset \cr} $$
